The “Full Moon” Thing

Almost every story being written about ISON – in a newspaper, on a website, on a blog – is screaming, with all the excitement of a fat kid locked in a sweetshop, that it might shine “As bright as the Full Moon!!!!” Some are even saying it will be FIFTEEN TIMES BRIGHTER than the Full Moon!!!! (I watched one YouTube clip with someone – with absolutely no grasp of astronomy, or grip on reality it seems – suggesting that the comet must be HUGE if it’s going to shine that big in the sky, and that the Powers That Be aren’t telling us how big it really is… ) That’s leading to a lot of people expecting Comet ISON to look something like this…

Look at THAT!!!! OMG!! That’s SO amazing!!! I can’t WAIT to see that!! That will be INCREDIBLE!!!

Sigh. Every time I read a headline like that I want to scream, or reach into my computer screen, grab its writer by the throat and shake them like a rag doll whilst shouting in their swiftly-reddening face “NO IT WON’T!!!! STOP REPEATING RUBBISH!!!!”

Because this is a misconception that has taken on an almost mythical quality. In years to come, when astronomy historians look back at ISON, I fear that, whatever it eventually looks like, it will be known as “that comet that everyone said would be as bright as the Full Moon”.

As the great woman said… Listen very carefully, I shall say this only once...

Comet ISON will NOT blaze as brightly as the Full Moon in our sky.

Actually, having said that, statistically speaking it might “be” as bright as the Moon, in astronomical terms, i.e. if it was measured scientiofically, but it won’t look anything LIKE the Moon, which is what all these badly- and lazily-written stories are leading people to believe, and there’s a HUGE difference.

What’s the truth behind this then? It has to have ome from somewhere, right?

Well, astronomers have been calculating Comet ISON’s path feverishly ever since its discovery, and their calculations suggest that IF certain things happen then there’s a chance that the comet’s maxium magnitude – its greatest brightness – would be the equivalent of the brightness of the Full Moon. That sounds brilliant when you read it, admittedly. But wait…

That maximum brightness will occur when the comet is at its closest to the Sun, so the two would appear next to each other in the sky, so we might have a comet that’s technically as bright as the Moon next to the Sun in the sky –

There. That’s it. I think you got it. Now do you see the fault with this whole “Full Moon” thing?

If a lightbulb didn’t go on above your head that’s ok, just take a moment to think about that, I’ll wait for you…

…….

…….

Yep, NOW you’ve got it. Now can you see why ISON will not blaze as bright as the Moon in the sky…! That’s why it won’t look like this after it has rounded the Sun and is about to climb up into the northern hemisphere’s evening sky…

If you didn’t get it, then let me make it clearer:

THE SUN IS INCREDIBLY, UNBELIEVABLY, STUPIDLY BRIGHT!!!!!

So, if you could magically grab the Full Moon and place it next to the Sun in the sky, how bright would the Moon look?

That’s right, the incredible brightness of the Sun would all but drown it out.

And THAT’s why we won’t see a “brighter than the Moon” comet blazing in our sky.

Of course, there’s a good chance that ISON will get very impressively bright, bright enough to be an absolutely beautiful object in the sky after dark, with a long, long tail like a searchlight, but we don’t even know that yet, and won’t know that for a while. But the Full Moon thing?

I’m sorry. I’m so, so sorry. But that won’t happen.

BUT…

When ISON is at its closest to the Sun – and “closest” is very close indeed – on Nov 28/29th, and if it does indeed shine at the same magnitude as the Mo0n, we might be able to see it, looking like a bright spark or something similar close to the Sun. Perhaps blocking out the Sun with your hand, or hiding it behind the wall of a building would bring it in to view, like this…

…but I’m also wondering if it would be possible to see it with the naked eye when the Sun is low and dimmed by the murk and mist and atmospheric haze that lingers above the horizon…? If it would be, perhaps, just perhaps, it might look like this on the morning of the 29th of November, once it has rounded the Sun…?

And then, at the end of the day, when the Sun is low, might we see this..?

Or dare we hope for something as good as this…?

There’s no way of knowing. Those views might all be wildly optimistic, and I AM NOT SAYING COMET ISON WILL LOOK LIKE THIS, but we can always hope, can’t we?🙂

But no, Comet ISON will NOT look like another Moon in the sky.

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10 Responses to “The “Full Moon” Thing”

After we’re done with that “full moon” thing (you didn’t name the specific British newspaper article that was the main source for this misleading meme), another misconception has to go as well that’s widespread even among astronomers: that only a bright comet – i.e. one with a coma (head) rivalling the planets in brightness – could become a ‘great’ comet with a stunning (dust) tail.

We actually had several striking counterexamples in the past decades and even years where the coma had already faded dramatically when the tail delivered the best performance: West was such a case in March 1976, McNaught in January 2007 and Lovejoy in December 2011. The latter actually didn’t have a head at all anymore (that had fallen apart just after perihelion) when it showed its wondrous tail around X-mas 2011.

When ISON emerges from perihelion in early December this year and steps into dark skies again, its coma will have faded enormously already, perhaps below zero magnitude. But hopes – and expecations amongst many experts – are that it will develop a dramatic dust tail at that time, a kind of Lovejoy on steroids, which fades only slowly while the coma is nearly gone.

West, McNaught, and Lovejoy are excellent examples … and there is still another comet to compare – Comet Kirch (C/1680 V1), also known as “The Great Comet of 1680”. Its orbit parameters are nearly identical with that of ISON, and it swung around the sun at the same time of the year (Dec 18 againts Nov 28). It was visble in daylight at the sun’s rim, maybe as bright as -10 mag. But its big time came only a few days later, around Christmas 1680. At that time it was surely down to 0 or +1 mag, but it developed an incredible tail stretching out to a length of about 90°. This was the thing that caused fear and panic among the superstitous people of the time. It was not bright as the moon, even not as bright as the brightest stars, but it was huge. Comet Kirch was more impressive than any of the Kreutz sungrazers including the “Daylight Comet” of 1843; as far as I can see during the last 500 years C/1680 V1 was only (and by far) surpassed by the incredible comet of 1861. That one loked like the materialization of medieval nightmares, but it came in the 19th century and caused no panic, just amazement. Yes, ISON can develop into one of the most impressive comets of history, but to cite a former US-president: “The tail its, stupid”.

[…] bright as the full moon” and be visible to the naked eye during the day. However, according to Stuart Atkinson at Waiting for ISON, saying that ISON will be as bright as the full moon is misleading. Atkinson points out that […]

[…] The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don’t believe everything you read. […]

[…] The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don’t believe everything you read. […]

[…] The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don’t believe everything you read. […]

[…] The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don’t believe everything you read. […]

[…] The former object will be at its brightest in March this year, and may be as bright as Venus. Comet ISON has the potential to be even more exciting, with many headlines screaming “Comet to be brighter than the Full Moon!”, although don’t believe everything you read. […]

I heard the moon has flipped upside down..🙂 just kidding. I know how much you hate that. I am slightly concerned with the solar maximum and the seemingly increased flare-up activity of the sun when these sun-grazers fly by… this will be a slightly larger comet than the last 2, should we expect increased CMEs? Or, is that part of the ongoing scientific question being explored by professional astronomers.

As far as I know there is no evidence of comets triggering CMEs. Lovejoy, which passed much closer to the Sun that ISON will, didn’t cause any, so no reason to believe ISON will at month’s end. The Sun is very active at the moment because it is solar maximum, and it was always going to be active at this time. Just a coincidence that ISON is in the area🙂